testsuite: Fix incorrect -mfloat128-type option

testsuite: Fix incorrect -mfloat128-type option

This test currently fails with an error about -mfloat128-type being an
invalid option, which is not what it's supposed to be testing:

XFAIL: gcc.target/powerpc/ppc-fortran/pr80108-1.f90   -O  (test for excess errors)
Excess errors:
xgcc: error: unrecognized command-line option '-mfloat128-type'; did you mean '-mfloat128'?

With this change we get the error that the comment says it expects:

XFAIL: gcc.target/powerpc/ppc-fortran/pr80108-1.f90   -O  (test for excess errors)
Excess errors:
f951: Error: power9 target option is incompatible with '-mcpu=<xxx>' for <xxx> less than power9
f951: Error: '-mfloat128' requires VSX support
f951: Error: '-m64' requires a PowerPC64 cpu

gcc/testsuite/ChangeLog:

	* gcc.target/powerpc/ppc-fortran/pr80108-1.f90: Change
	-mfloat128-type to -mfloat128.